The invention relates to the art of polybenzazole polymers.
Polybenzazole (PBZ) polymers are well-known and described in numerous literature references, such as 11 Encyclopedia of Poly. Sci & Eng., Polybenzothiazoles and Polybenzoxazoles, 601 (1988), which is incorporated herein by reference. Mer units in polybenzazole polymers are ordinarily either AB-units, as illustrated in Formula 1(a) or AA/BB-mer units, as illustrated in Formula 1(b): ##STR1## wherein:
each Ar is an aromatic group,
DM is a divalent organic moiety which is stable and inert in acid under polymerization conditions, and
each Z is independently an oxygen atom, a sulfur atom, or a nitrogen atom that is bonded to a hydrogen atom or an organic moiety which is stable and inert in acid under polymerization conditions.
(For the purpose of this application, when the nitrogen atoms and Z moieties of a mer unit are depicted as bonded to an aromatic group without indicating their position, as in Formulae 1(a)-(b), it shall be understood that:
(1) each nitrogen atom and Z group within a given azole ring are bonded to the aromatic group in ortho position with respect to each other: and PA1 (2) if the mer unit has two azole rings, one nitrogen atom and Z moiety may be in either cis position or trans position with respect to the other nitrogen atom and Z moiety, for example illustrated in 11 Ency. Poly. Sci. & Eng., supra, at 602, which is incorporated herein by reference.The same understandings apply with respect to amine groups and Z moieties in a BB-monomer.)
Polybenzazole polymers may be rigid rod or semi-rigid polymers which can sometimes form liquid crystalline dopes in solvent acids. Such polymers are noted for their high thermal stability and resistance to common organic solvents. However, the polymers are frequently difficult to fabricate into a useful article because they are not always thermoplastic, they are often insoluble in common organic solvent, and they are incompatible with many thermoplastic polymers.
Polybenzazole polymers have been modified by placing flexible moieties in the polymer backbone, in order to render the polymers thermoplastic or compatible with other polymers. However, many common flexible moieties which are put into polybenzazole polymers lower the thermal stability or solvent resistance of the polymer.
What are needed are polybenzazole polymers containing flexible moieties which have high thermal stability and/or solvent resistance.